By Nicole Chavez, Eric Levenson and Joe Sterling, CNN

(CNN) -- Hurricane Harvey was "dangerously approaching the Texas Coast" Friday morning, expected to drop as much as 35 inches of rain and usher in "life-threatening" storm-surge flooding upon landfall late Friday or early Saturday, the National Hurricane Center said.

The combination of heavy rain, storm surge, flooding and strong winds could leave wide swaths of South Texas "uninhabitable for weeks or months," the National Weather Service in Houston said, employing daunting language not seen by CNN's experts since Hurricane Katrina, which left more than 1,800 people dead in 2005.

As heavy rain and gusty winds move in over Texas, coastal residents were deciding Friday whether to flee or to stay put and brace for a potentially deadly hurricane.

Conditions are "expected to deteriorate through the day," the hurricane center said. "Preparations along the middle Texas coast should be rushed to completion this morning."

Harvey, now a Category 2 hurricane, is on track to strengthen to Category 3, with winds of at least 111 mph by the time it makes landfall around Corpus Christi," forecasters say. The storm is then expected to stall, broadening the flood threat across Texas and the South, forecasters said.

TRACK THE STORM

"All indications from the hurricane center are that this is going to be the first major hurricane the nation has dealt with since 2005," FEMA Director Brock Long said.

Latest developments

-- Harvey strengthened early Friday, becoming a Category 2 hurricane with winds up to 110 mph, according to the National Weather Service.

-- Isolated tornadoes are possible Friday across portions of the middle and upper Texas coast, the service said.

-- Texas Gov. Greg Abbott has requested the activation of 700 National Guard members.

-- The Ports of Corpus Christi and Galveston are closed.

-- Three Galveston-based cruise ships in the Gulf of Mexico diverted to safer water.

FEMA prepared for 'significant disaster'

"Texas is about to have a very significant disaster," Long, the FEMA chief, said, stressing that people need to heed evacuation warnings.

Those who stay should "elevate and get into a structure that can withstand potentially Category 3 winds from a hurricane," he said.

"The bottom line message is, right now, if people have not heeded the warning, again, their window to do so is closing," Long said. "If they refuse to heed the warning, that's on them."

Long said he is "very worried" about storm surge, or "wind-driven water," slamming coastal areas, saying it has the "highest potential to kill the most amount of people and cause the most amount of damage."

A "significant inland flood event over many counties" is expected, he warned.

"Over the next five days, we're going to see copious amounts of rainfall, up to 25 inches, possibly, in some areas, with isolated higher amounts," he said. "This is going to be a slow-developing major disaster event for the state of Texas."

FEMA has pre-positioned incident management teams, as well as life-saving and life-sustaining commodities, and search-and-rescue teams in Texas, Long said.

Long said FEMA is "fully engaged" with the White House, as Harvey is poised to deliver a critical test of President Donald Trump's abilities as commander-in-chief.

"I think we'll be looking at the potential request for presidential disaster declarations coming up from Gov. Abbott," Long said. "The President has the ability, has the authority to sign off on those to mobilize our support to the state governments."

Harvey is also causing concern in New Orleans, where heavy rain could usher in as much as 20 inches of rain through early next week and overwhelm the city's already-compromised drainage system.

'I'm trying to be strong'

The threat of Harvey became evident Thursday when several counties on the Texas coast issued evacuation orders -- and an exodus of residents began.

Drivers sat bumper-to-bumper, with highways backed up for miles.

Rose Yepez told CNN it took her twice as long as usual to drive 140 miles from Corpus Christi to San Antonio, en route to Texas Hill Country.

Private vehicles -- along with city buses packed with adults and children carrying backpacks -- jammed roads for hours.

"I'm shaking inside, but for them, I'm trying to be strong," a Corpus Christi woman who was waiting with her two daughters to board a bus out of town told CNN affiliate KRIS.

Ambulances stayed busy overnight, and 10 critically ill babies were evacuated to North Texas on medical flights from a Corpus Christi hospital, the Cook Children's Hospital in Fort Worth said in a statement.

Workers at 39 offshore petroleum production platforms and an oil rig in the Gulf of Mexico also evacuated Thursday, the Bureau of Safety and Environmental Enforcement said.

Staying put, boarding up

Meantime, first responders, like Brittany Fowler, stayed behind and waited for the storm.

"Hopefully it doesn't do any damage, but if it does, we've prepared," Fowler, a firefighter in Corpus Christi, wrote on Instagram.

Fowler's family helped by boarding up windows and doors at her home, and she bought plenty of water, food and a small power generator.

Corey Davis, by contrast, was free to go -- but opted to stay put, even as Harvey's winds started blowing Thursday night. Instead of packing, she and her relatives took turns climbing a tall ladder to secure plywood over windows at their Port O'Connor home.

"I'm scared, so I'm doing everything that I can to protect (this) little place down here," Davis told CNN affiliate KTRK, "and hope and pray for the best."